6.2 使用弹出菜单:Popup类
并不是我们希望弹出的所有内容都需要是一个菜单。通过Popup与PopupFactory类,我们可以在其他的组件上弹出任何组件。这与工具提示不同,工具提示是只读的不可选择的标签。我们可以弹出可选择的按钮,树或是表。
6.2.1 创建弹出组件
Popup是一个具有两个方法hide()与show()的简单类,同时具有两个受保护的构造函数。我们并不能直接创建Popup对象,而是需要由PopupFactory类获取。
- PopupFactory factory = PopupFactory.getSharedInstance();
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Popup popup = factory.getPopup(owner, contents, x, y);
由PopupFactory所创建的带有contents组件的Popup则会位于owner组件内的其他组件之上。
6.2.2 一个完整的Popup/PopupFactory使用示例
列表6-7演示了在另一个JButton之上显示了一个JButton的Popup与PopupFactory的使用示例。选择初始的JButton会使得在第一个JButton之上,在随机位置创建第二个。当第二个按钮可见时,每一个都是可选择的。多次选择初始的可见按钮会出现多个弹出按钮,如图6-9所示。每一个弹出菜单将会在三秒后消失。在这个例子中,选择弹出菜单只会在控制台显示一条消息。
- package net.ariel.ch06;
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import java.awt.Component;
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import java.awt.EventQueue;
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import java.awt.event.ActionEvent;
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import java.awt.event.ActionListener;
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import java.util.Random;
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import javax.swing.JButton;
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import javax.swing.JFrame;
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import javax.swing.Popup;
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import javax.swing.PopupFactory;
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import javax.swing.Timer;
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public class ButtonPopupSample {
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static final Random random = new Random();
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// define ActionListener
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static class ButtonActionListener implements ActionListener {
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public void actionPerformed(ActionEvent event) {
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System.out.println("Selected: "+event.getActionCommand());
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}
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};
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// define show popu ActionListener
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static class ShowPopupActionListener implements ActionListener {
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private Component component;
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ShowPopupActionListener(Component component) {
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this.component = component;
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}
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public synchronized void actionPerformed(ActionEvent event) {
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JButton button = new JButton("Hello, world");
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ActionListener listener = new ButtonActionListener();
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button.addActionListener(listener);
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PopupFactory factory = PopupFactory.getSharedInstance();
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int x = random.nextInt(200);
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int y = random.nextInt(200);
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final Popup popup = factory.getPopup(component, button, x, y);
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popup.show();
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ActionListener hider = new ActionListener() {
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public void actionPerformed(ActionEvent event) {
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popup.hide();
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}
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};
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// hide popup in 3 seconds
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Timer timer = new Timer(3000, hider);
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timer.start();
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}
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};
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/**
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* @param args
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*/
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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Runnable runner = new Runnable() {
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public void run() {
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// create frame
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JFrame frame = new JFrame("Button Popup Sample");
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frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
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ActionListener actionListener = new ShowPopupActionListener(frame);
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JButton start = new JButton("Pick Me for Popup");
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start.addActionListener(actionListener);
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frame.add(start);
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frame.setSize(350, 250);
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frame.setVisible(true);
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}
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};
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EventQueue.invokeLater(runner);
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}
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}
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